lec9.docx

**Faculty of Dental medical** **Lecture : 9** **Gram positive cocci** A. - **General features of staphylococcus** 1. There is more than 40 species of staphylococcus , only 3 medical important ( s. aureus , s. epidermidis, s. saprophyticus ) 2. Gram positive Cocci and arranges in pair...

**Faculty of Dental medical** **Lecture : 9** **Gram positive cocci** A. - **General features of staphylococcus** 1. There is more than 40 species of staphylococcus , only 3 medical important ( s. aureus , s. epidermidis, s. saprophyticus ) 2. Gram positive Cocci and arranges in pair chin or cluster ( grape like) 3. Facultative anaerobes bacteria and grow on simple media 4. Catalase Positive ( H~2~O~2~ H~2~O + O~2~ ) ***Staphylococcus aures*** **Morphology :** Gram positive cocci arranged in clusters , some strains capsulated. **All cocci** are non motile and non spore forming **Culture ( cultivation ):** can grow in nutrient agar and blood agar in 37c for 24h. **Grow in large yellow golden colonies on nutrient agar ( *aures* = gold )**  **And it is B hemolytic on blood agar** Ferment the manitol sugar in manitol salt agar( selective media ) and produce acid  **Virulence factors :** - **Surface adhesions :** allow the bacteria to adhere to host tissues and form biofilm that provide protection from host defenses and antimicrobial agents - **Coagulase :** an enzyme that converts fibrinogen into fibrin and make **protective** **fibrin clot** around the bacteria , this clot shields the bacteria from phagocytosis - **Leukocidin :** destroys White Blood Cells - **Catalase enzyme :** ( H~2~O~2~ H~2~O + O~2~ ) when macrophage eat bacteria it produce a H~2~O~2~ to kill it but *S. aureus* break it by produce catalase enzyme. - **Nucleases :** DNase & RNase - **Protein A :** bind to antibody and prevent the killing of bacteria. allow *S.aureus* to evade the immune response - **B lactamase** - **Exotoxin :** 1. Enterotoxin ( food poisoning ) 2. Exofoliative toxin ( scalded skin syndrome ) 3. Toxic shock syndrome toxin ( TSST) **Diseases by *S.aureus.*** *S.aureus* inhabit in skin & mucous membrane and in nasal mucousa ( 40% - 50% ) of people. **Some of the common diseases associated with *S.aureus*** a. **Skin and soft tissue infection** such as impetigo , pus , red , swollen , and painful areas on the skin b. **Staphylococcal scalded skin syndrome ( SSSS) :** Is severe skin infection caused by *s.aureus* that produce exfoliative toxins characterized by wide spread skin redness, and skin peeling resembling a scalding burn  c. **Toxic shock syndrome toxin (TSST) :** this toxin has 2 target ( blood vessel, GIT) In blood vessel make vasodilation leading to drop in blood pressure, GIT leads to vomiting & diarrhea this type of toxin happen by using a contaminated tampons in menstrual cycle and also happen by contamination of surgical instruments. This type of toxin leads to a fever ,multi organ dysfunction leading to life threating d. **Bacteremia and Endocarditis :** can cause bloodstream infectios (**Bacteremia** ) e. **Pneumonia.** f. **Food poisoning :** 50% of staph aureus produced enterotoxin, characterized by ( heat stable, short I.P period of 1-6 hrs , gut resistant ) and cause Nausea, vomiting , diarrhea without fever. Self limiting after 24h ( cure ) **Lab. diagnosis of *Staph.aureus*** i. **Specimen** ii. **Direct smear** iii. **Cultivation** iv. **Identification** v. **Toxin ( FP,TSST, SSSS)** **Specimen :** Swap from lesions , pus , sputum ,CSF, blood culture ( Acute endocarditis), urine culture (UTI) **Direct smear :**  **Cultivation :**on Nutrient agar or blood agar at 37c for 24h. **Identification :** on Nutrient agar , the colonies are Golden yellow colonies or blood agar B hemolysin colonies. **Colonies Identified by :-** 1. Gram staining  2. **Catalase test** H~2~O~2~ H~2~O + O~2~ 3. **Manitol salt agar :** has indicator called phenol red , when the colony ferment the manitol sugar produce acid that called a s. aureus colony  **Food poisoning diagnosis (FP)** - Cultivate the vomiting or diarrhea on Manitol Salt Agar (Selective media). - By ELISA **Toxic Shock Syndrome diagnosis (TSS) :** take the specimen from **tampon** or **vaginal swab** or **serum** after that cultivated on MSA for **24h** at **37c**. or by ELISA trough serum. **Scalded Skin Syndrome (SSS) :** direct smear from Bullae. **Treatment:** 95% of S. aureus Resistant to penicillin so they made a semi -- synthetic penicillin ( Methicillin , Oxacillin, Nafcillin) , after years S. aureus become Resistant to Methicillin and called MRSA, after years become Resistant to vancomycin and called VRSA. The active medicine is linezolied ,Daptomucin. **Prevention :** No vaccine , hand washing , avoidance of sharing personal item. **S. epidermidis & S. sabrophytic both are :** - Grow in nutrient agar at 37c for 24h and appear a white colony or in Blood agar at 37c for 24h and appear a white colony ( non hemolytic ) - Grow in MSA and appear a Pink colony - Coaqulase (-) - Catalase (+) ***S. epidermidis*** Commonly found on human skin as normal flora , it can also act as opportunistic pathogen by - **Adherence** : by glycocalyx and adheres on device such as tooth - **B- lactamase producing** - **Wound infection** - **Other diseases such as** ( UTI , Sub acute Endocarditis, Arthritis ) ***S. sabrophyticus*** Found in soil & water , *S. sabrophyticus* attaches to genitourinary tract and cause **honeymoon cystitis** **Treatment :** ***S. epidermidis*** by Vancomycin , Gentamicin and ***S. sabrophyticus*** by Ciprofloxacin